AMES — Drought, extreme rains and flooding during the last five years greatly have influenced farmers' beliefs about climate change, according to the 2013 Iowa Farm and Rural Life Poll.

The annual survey once again took a close look at climate change and agriculture. It repeated questions that first were asked in 2011 to track changes in farmers' beliefs about whether climate change is occurring, and if so, what the causes might be, said J. Gordon Arbuckle Jr., a sociologist with Iowa State University Extension.

Arbuckle co-directs the annual poll with Paul Lasley, also an Extension sociologist.

Arbuckle said 1,209 farmers participated in the 2013 survey, and, on average, they were 65 years old. Because it is a panel survey, in which the same farmers participate in multiple years, participants are somewhat older on average than the general farmer population.

"There were some substantial shifts that occurred between 2011 and 2013," Arbuckle said. "The proportion of farmers who believed that climate change is occurring and due primarily to human activities increased from 11 percent to 16 percent, while the percentage who indicated that there is not enough evidence to know with certainty that climate change is occurring dropped from 27 percent to 23 percent."

Arbuckle said that there only were slight changes, one or two percentage points, in the other categories: That climate change is caused mostly by natural changes in the environment, it's caused more or less equally by natural changes and human activities or it isn't occurring at all.

"We asked farmers to rate the influence that several factors might have had on their beliefs about climate change over the past five years," Arbuckle said.

Forty-nine percent indicated that drought had been a moderate or strong influence on their beliefs about climate change, and 41 percent said the same about extreme rains and flooding.

"I kind of expected that," Arbuckle said. "Iowa has experienced numerous weather extremes over the last several years, with excessive rain, floods, drought and temperature volatility leading to significant impacts on agricultural productivity. Extreme weather events are predicted to become more common in Iowa and across the Corn Belt in the future. Scientists are predicting that climate change will have a number of negative effects on Iowa agriculture, so farmers also were asked the degree to which they are concerned about some of those potential impacts.

At the time of the survey, February 2013, all of Iowa was considered to be in moderate to extreme drought.

"Not surprisingly, two-thirds of farmers rated 'longer dry periods and drought' as their highest concern," said Arbuckle. "Farmers are definitely worried about some of the impacts that scientists are predicting for Iowa."

Sixty percent indicated they were concerned or very concerned about increased insect pressure and soil erosion. Similar percentages were concerned or very concerned about increases in heat stress on crops (59 percent), weed pressure (58 percent) and crop diseases (56 percent).

Farmers were less concerned about some water-related threats. Forty-nine percent were concerned or very concerned about increases in loss of nutrients into waterways. More frequent extreme rains was a concern for 44 percent, 33 percent had concerns about saturated soils and 25 percent had concerns about flooding.

About half of farmers in both surveys agreed or strongly agreed that extreme weather events will happen more frequently in the future. Forty-four percent of the respondents in both years agreed that they were concerned about the potential effects of climate change on their farm operations.